Let's just add a rule: if an opponent disconnects frequently (more than once), you can decline a match with them without explanation (due to suspicion).

In my opinion, it's not worth suspecting an opponent of cheating if they have frequent disconnections due to internet issues. Most likely, they are not doing it intentionally. I myself have often experienced situations where the internet connection was poor, and disconnections occurred frequently, even during battles. I'm glad that almost no one suspected me of cheating because of this. (Although it was embarrassing.) And why would they frequently simulate disconnections? They're not losing that often.